1. Field of the Invention
The present invention relates to a data transmitting apparatus, and more particularly to a data transmitting apparatus which is capable of efficiently transmitting data in a mixed mode.
2. Description of the Related Art
There have been proposed various communication systems for document data, one being a system such as a telex in which a document composed entirely of characters are encoded into character data to transmit such a document in a highly efficient manner, and the other being such a system as a facsimile capable of transmitting a document containing an arbitrarily selected picture image data which cannot be encoded by the above-mentioned character encoding system.
The two systems mentioned above are different from each other in the encoding processes, and yet have some common features. For example, a protocol system is used in both a facsimile and a telex in the Group 4 (G4) category. As the result of such a common feature, a mixed mode communication system, which integrates these two processes, has come to be realized. With such a mixed mode communication system, it is possible to perform highly efficient transmission of documents which contain image data and character data in a mixture.
That is to say, it would take a long transmitting time to make an attempt at transmitting a document entirely in the form of picture image data because such a process would involve a larger amount of data, but a mixture of character data which can be transmitted in a set of codes for each character will be able to attain a reduction of the amount of data to be transmitted and therefore a reduction of the transmitting time as compared with a case in which the entire document is transmitted uniformly as picture image data.
In this regard, the G4 facsimile mentioned above is available in Class 1, which can transmit and receive only picture image data, Class 2, which can receive character data in addition to the transmission and reception of picture image data, and Class 3, which can transmit and receive both picture image data and character data.
Therefore, even communications between G4 facsimile units may fail in transmitting character data in some cases in which the receiving facsimile unit, for example, has only the functions of Class 1.
In an effort to deal properly with a trouble like this, the apparatus which is described in Published Unexamined Japanese Patent Application No. sho-61-252740 published in 1986 is designed to be capable of converting character data to picture image data to be transmitted to the receiving station having no capability of displaying or printing a document on the basis of received character data (this capability is hereinafter referred to as "the receiving capability").
As described above, there is some problem in the communication in the mixed mode that the process still takes a longer communication time than in the transmission of character data only, though it can certainly reduce the communication time and that particularly in case there are many vacant spaces in the image data part, also such vacant spaces are transmitted as a part of the picture image data, with the result that much wasteful communication time has to be spent.
Now, this problem will be shown specifically with reference to an example of a document shown in FIG. 5. A single page of this document is composed of three blocks A, B and C. Of these, the blocks A and C are blocks composed of character data while the block B is a block composed of picture image data.
At this point, attention is paid to the block B, which contains image data, and it is observed that a large vacant space V is present in the central part of the block B. In spite of the fact that there is such a vacant space in it, the block B which represents picture information read with a reading device as a coherent set of figures and tables and pictures, is stored in the memory as continuous image data including the vacant space V from a start point B0 to a termination point B1. Accordingly, wasteful time would be needed for the communication of the image data thus containing such vacant spaces.
In such conventional communications of data in a mixed mode, such wastefulness as this still remains without any improvement made upon it.